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10.3: Change Ethernet MAC address from the Terminal
Authored by: mnb on Nov 09, '03 06:17:11PM

I'm sure there must be some legit reason to need to change your MAC address, but I can't think of one offhand. I can think of a few reasons that aren't legit, however...

1 - to allow access to a network that is controlled by MAC address.

2 - to bypass identification methods that use the MAC address as your machine's unique identifier. Some applications use this, it's rumored ITMS does. This is, in essence, VERY similar to the first reason...

MAC addresses are supposed to be like public IPs, that is... UNIQUE. Allowing people to change them defeats the purpose of having them.



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10.3: Change Ethernet MAC address from the Terminal
Authored by: MacOSXAddict on Nov 10, '03 09:05:37AM

Don't forget, to modify your mac address so you can use your brand new machine on your cable modem without goint through the hassle of informing the ISP of the MAC change...

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Bob



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10.3: Change Ethernet MAC address from the Terminal
Authored by: Crawdad on Nov 12, '03 11:43:47AM

Not all MAC addresses are expected to be unique across the world. If the second-lowest bit of the first octet is set, the address is "locally administered" and not assumed to be worldwide-unique.

Warning! If you set the lowest-order bit of the first octet to a "1" (in other words, if the first byte is odd) strange and bad things may happen, because that indicates an ethernet multicast address. In a very small network envirnment you might not notice, but elsewhere it may bite you.



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10.3: Change Ethernet MAC address from the Terminal
Authored by: urilabob on Apr 05, '06 08:45:49AM

Let me give a legitimate reason. I have just spent ~40 hours debugging a problem with MAC address allocation in a Fedora Core 5 intel box. Strange behaviour - it could establish a network connection and run services such as ssh, but persistent connections such as http and sftp failed. The _only_ reason I was finally able to narrow it down to MAC addresses was that I found this thread, and discovered how to reset my powerbook's MAC address. I was then able to exactly duplicate the FC5 box's network settings on my PB. Lo and Behold, it _didn't_ have the problem - so that meant it was a problem in the box, not with the setup of the network itself. Shortly afterward, I deduced that it had to be the MAC address itself. Turns out that if you set the MAC address under FC5 in upper case - AA:BB:CC:DD:EE:FF - it screws up, at least with my driver. If you set it up in lower case - aa:bb:cc:dd:ee:ff - it works fine. I assume that the driver returns lower case, and some stupid code somewhere is case-sensitive and returns a mismatch if upper case is entered. I doubt I would _ever_ have found this bug, and would have continued to blame the problem on my network managers, if not for this thread.



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